Better CSS for bootswatch themes

[robertgarrigos]

Later release improves the css for dropdown buttons. However, some tables for dark themes don't show exactly as the bootswatch theme, specially when they include a dropdown button.

This is how a dropdown button show within a table in Cyborg theme:

This is a proposal for the dropdown more like the original Cyborg bootswatch show a dropdown button (not in a table, though) (https://bootswatch.com/3/cyborg/#tabs):

What color version do you like to have for the dropdown buttons within tables?

[bugfolder]

The second one definitely looks better.

[robertgarrigos]

This PR improves tables and dropdowns for all bootswatch themes.